Foundation pile installation method

Abstract

To provide a foundation pile installation method which has high workability and can suppress construction cost.SOLUTION: A foundation pile installation method includes the steps of: forming a lower hole 2 having a diameter D1 extending in a vertical direction to a ground 1; filling the lower hole with a cement-based solidification material 3; agitating the ground together with the lower hole within the range of a diameter D2 larger than the diameter D1, and thereby forming a columnar improvement body 4; and placing a foundation pile 5 into the columnar improvement body, before the columnar improvement body is solidified. The foundation pile installation method directly fills the lower hole with the cement-based solidification material, in other words, fills it with the cement-based solidification material as powder as it is without agitating the cement-based solidification material with improvement object soil. It is not necessary to produce cement milk on the ground surface like the conventional art, and to agitate the cement-based solidification material with the improvement object soil on the ground surface, which can improve workability and can suppress construction cost.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for installing foundation piles for use in ground installations. [Background technology]

[0002] For example, Patent Document 1 discloses a method for installing foundation piles for use in aboveground installations such as solar power generation facilities, which involves the steps of forming a cylindrical pile hole with a diameter larger than the outer diameter of the foundation pile, injecting cement milk into the pile hole, forming a columnar improved body using soil cement made by stirring and mixing excavated soil and cement milk, and pressing the foundation pile into the columnar improved body before the soil cement hardens, and injecting cement milk between the columnar improved body and the foundation pile.This method allows the cement milk to fill any gaps that occur between the columnar improved body and the foundation pile, resulting in a stable foundation pile structure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-108279 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology disclosed in Patent Document 1 above has the problem that the processes of mixing cement-based solidification material and water on-site to produce cement milk and injecting cement milk into pile holes, etc., are cumbersome and result in increased costs.

[0005] In consideration of such problems, the present invention aims to provide a method for installing foundation piles that is easy to install and can reduce construction costs. [Means for solving the problem]

[0006] [First invention] The method for installing foundation piles of the present invention is characterized by comprising at least the steps of forming a pilot hole with a diameter D1 extending vertically into the ground, filling the pilot hole with a cement-based solidification material, forming a columnar improvement body by stirring the ground together with the pilot hole within a range of diameter D2 larger than diameter D1, and driving a foundation pile into the columnar improvement body before the columnar improvement body solidifies. [Second Invention] The foundation pile is also characterized by having a rod-shaped main body and a plurality of wings extending in the circumferential direction of the main body.

[0007] [Third Invention] The method for installing foundation piles of the present invention is characterized by comprising at least the steps of forming a pilot hole extending vertically into the ground, filling the pilot hole with a cement-based solidification material, and rotating a pile having spiral drilling wings around a rod-shaped main body as a foundation pile around its axis while screwing it into the pilot hole, thereby allowing the cement-based solidification material filled in the pilot hole to penetrate into the ground around the pilot hole.

[0008] [Fourth Invention] The method for installing foundation piles of the present invention comprises at least the steps of forming a pilot hole extending vertically into a ground where a gravel layer exists underground, down to the gravel layer, filling the pilot hole with cement-based solidification material, and using a foundation pile having spiral drilling wings around a rod-shaped main body as a foundation pile, rotating the foundation pile around its axis until the tip of the foundation pile reaches the gravel layer, thereby screwing the foundation pile filled in the pilot hole into the gravel layer.

[0009] [Fifth Invention] The method for installing foundation piles of the present invention is characterized by conducting a boring survey of the ground, and if a gravel layer is not present in the ground, adopting any of the methods of the first to third inventions above, and if a gravel layer is present in the ground, adopting the method of the fourth invention above. [Effects of the Invention]

[0010] One of the features of the first to fifth inventions is that the cement-based solidification material is directly filled into the pilot hole, that is, the cement-based solidification material is filled in powder form without being mixed with the soil to be improved. This eliminates the need to produce cement milk on the ground surface or mix the cement-based solidification material with the soil to be improved on the ground surface, as in the conventional technology, thereby improving workability and reducing construction costs.

[0011] In the first invention, the prepared hole filled with cement-based solidification material and the ground surrounding the prepared hole are simultaneously stirred to form a columnar improved body. Since the foundation pile is installed on the columnar improved body, the foundation pile can be firmly fixed even in soft ground. It is preferable that the foundation piles have wings, as in the second invention. Since the foundation piles are driven before the columnar improvement body solidifies, the wings on the foundation piles provide resistance (anchors) and allow them to remain upright.

[0012] In the third invention, the cement-based solidification material filled in the pilot hole is pushed outward by the foundation pile and penetrates into the ground. The cement-based solidification material reacts with the moisture in the soil around the pilot hole and hardens, and the moisture in the soil then penetrates into the pilot hole and hardens the cement-based solidification material around the foundation pile, thereby firmly fixing the foundation pile to the pilot hole.

[0013] In the fourth invention, the cement-based solidification material filled in the pilot hole is pushed outward by the foundation pile, penetrating into the ground. The cement-based solidification material also penetrates into the gravel layer below the pilot hole, reacting with the moisture in the soil and gradually solidifying, firmly fixing the tip of the foundation pile to the gravel layer. Furthermore, the cement-based solidification material is also present around the main body (between the excavation wings), and the moisture in the soil penetrates into the pilot hole and solidifies the cement-based solidification material present around the foundation pile, firmly fixing the foundation pile to the pilot hole.

[0014] In the fifth invention, the methods of the first to fourth inventions are made optional, and an appropriate method can be adopted based on the results of a boring survey of the ground at the construction site. This makes it possible to handle soft ground, hard ground, and hard ground with a gravel layer, improving workability. [Brief explanation of the drawings]

[0015] [Figure 1] 1A to 1D are diagrams illustrating a method for installing foundation piles according to a first embodiment. [Figure 2] 10A to 10D are diagrams illustrating a method for installing foundation piles according to a second embodiment. [Figure 3] 10A to 10D are diagrams illustrating a method for installing foundation piles according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] [First embodiment] A first embodiment of the foundation pile installation method of the present invention will be described. If the results of the boring survey reveal that there is no gravel layer in the ground, for example, if it is found that the ground is soft and no gravel layer exists, a pilot hole 2 with a diameter D1 extending vertically into the ground 1 is drilled as shown in Figure 1(a). Soft ground refers to ground that contains a lot of sandy soil or clay, has weak soil strength, and is durable and compressible. Examples of how to determine whether ground is soft include, but are not limited to, clay soil with an N value of 3 or less and sandy soil with an N value of 5 or less.

[0017] The means for forming the pilot holes 2 is not particularly limited, but for example, an earth auger may be used. Next, as shown in Figure 1(b), the prepared hole 2 is filled with cement-based solidification material 3. After filling the prepared hole 2 with the cement-based solidification material 3, it is preferable to tap the surface of the cement-based solidification material 3 to increase the filling density, and then fill more cement-based solidification material 3 into the area where the surface has sunk. If the ground contains a large amount of moisture, for example, a sheath pipe may be inserted into the prepared hole 2 and the inside of the sheath pipe may be filled with the cement-based solidification material 3.

[0018] Cement-based solidification materials 3 are often used for the purpose of improving soft ground with high efficiency, and refer to materials that contain cement as a base material and various active ingredients added. A known cement-based solidification material 3 is one that dehydrates and hardens the ground by utilizing its property of absorbing a large amount of water during hydration to form ettringite. An example of a cement-based solidification material 3 is the Eustabilar US60 series (manufactured by UBE Mitsubishi Cement Corporation). A commonly known construction method involves mixing the cement-based solidification material 3 with the soil to be improved on the ground surface and then backfilling it, but one of the features of this invention is that the cement-based solidification material 3 is directly filled into the pilot hole 2, that is, the cement-based solidification material 3 is filled in its powder form without being mixed with the soil to be improved.

[0019] Next, as shown in Figure 1(c), the ground 1 is stirred with a mixer 8 together with a pilot hole 2 filled with cement-based solidification material 3 within a range of diameter D2 larger than diameter D1 to form a columnar improved body 4. The size of the diameter D2 can be determined in consideration of the diameter D1 of the pilot hole 2, but if D1 is 150 mm to 200 mm, for example, the diameter D2 can be about 700 mm. Next, as shown in Figure 1(d), before the columnar improvement body 4 hardens, a foundation pile 5 is driven into the columnar improvement body 4. The cement-based solidification material 3 contained in the columnar improvement body 4 reacts with the moisture in the soil and gradually hardens. Once the cement-based solidification material 3 has completely hardened, the foundation pile 5 is firmly fixed in the soil.

[0020] As shown in Fig. 1(d), a foundation pile 5 having a rod-shaped main body 5a made of steel pipe and a plurality of wings 5b (two in this embodiment) extending in the circumferential direction of the main body 5a can be used as the foundation pile 5. Foundation piles 5 of this shape are commercially available. Because the foundation piles 5 are driven into the columnar improvement body 4 before it hardens, there is a risk that the foundation piles 5 may tilt inside the columnar improvement body 4, but by providing the wings 5b to the foundation piles 5, the wings 5b act as resistance (anchors) and allow the piles 5 to remain upright. Furthermore, by providing the wings 5b, the foundation piles 5 can withstand not only downward forces (pushing in) but also upward forces (pulling out). This completes the installation of the foundation piles 5.

[0021] [Second embodiment] A second embodiment of the method for installing foundation piles according to the present invention will now be described. If the results of the boring survey reveal that there is no gravel layer 7 in the ground 1, for example, if the ground 1 is soft or hard and no gravel layer 7 exists, a pilot hole 2 is formed extending vertically into the ground 1 as shown in Figure 2(a). Hard ground includes, for example, a gravel layer mixed with boulders and a bedrock layer, and an N-value of 50 or more is a guideline, but is not limited to this. If a gravel layer 7 exists in the ground 1, it is preferable to adopt the foundation pile installation method of the third embodiment described later.

[0022] There is no particular limitation on the means for forming the pilot hole 2, but for example, an earth auger may be used. There is no particular limitation on the diameter of the pilot hole 2, but for example, it may be about 120 mm. Next, as shown in Figure 2(b), the prepared hole 2 is filled with cement-based solidification material 3. After filling the prepared hole 2 with the cement-based solidification material 3, it is preferable to tap the surface of the cement-based solidification material 3 to increase the filling density, and then fill the area where the surface has sunk with more cement-based solidification material 3. One of the features of the present invention is that the cement-based solidification material 3 is directly filled into the prepared hole 2, that is, the cement-based solidification material 3 is filled in powder form without being mixed with the soil to be improved.

[0023] Next, as shown in Figure 2(c), a pile having a spiral drilling wing 6b around a rod-shaped main body 6a is rotated around its axis as a foundation pile 6, and screwed into the pilot hole 2, thereby penetrating the cement-based solidification material 3 filled in the pilot hole 2 into the ground 1 around the pilot hole 2. The cement-based solidification material 3 filled in the pilot hole 2 is pushed out to the surrounding area by the foundation pile 6, penetrates into the ground 1, reacts with the moisture in the soil and gradually solidifies. The cement-based solidification material 3 is also present around the main body 6a (between the excavation wings 6b), and the moisture in the soil penetrates into the pilot hole 2 and solidifies the cement-based solidification material 3 present around the foundation pile 6, so that the foundation pile 6 is firmly fixed to the pilot hole 2 as shown in Figure 2(d). This completes the installation of the foundation piles 6.

[0024] [Third embodiment] A third embodiment of the foundation pile installation method of the present invention will be described. If the boring survey reveals that a gravel layer 7 exists in the ground 1, a pilot hole 2 is drilled vertically into the ground 1, as shown in Figure 3(a), down to the gravel layer 7. Clay soil or sandy soil, for example, is often deposited on top of the gravel layer 7. A gravel layer refers to a stratum composed of gravels of 2.0 to 75 mm, and when a gravel layer is included, it is often considered hard ground. There is no particular limitation on the means for forming the pilot hole 2, but for example, a pecker may be used. There is no particular limitation on the diameter of the pilot hole 2, but it may be, for example, about 80 mm.

[0025] Next, as shown in Figure 3(b), the pilot hole 2 is filled with the cement-based solidification material 3. It is preferable to fill the cement-based solidification material 3 to a position several tens of centimeters below ground level (GL), and it is not necessary to hammer the surface of the cement-based solidification material 3. If the surface of the cement-based solidification material 3 is hammered to increase the packing density, the cement-based solidification material 3 may get into the gaps in the gravel layer 7, leaving no place for the cement-based solidification material 3 to escape when the foundation pile 6 is screwed into the pilot hole 2 in a later process. One of the features of the present invention is that the cement-based solidification material 3 is directly filled into the pilot hole 2, i.e., the cement-based solidification material 3 is filled in powder form without being mixed with the soil to be improved. Next, as shown in Figure 3(c), a pile having a rod-shaped main body 6a and spiral drilling wings 6b around it is used as the foundation pile 6, and the foundation pile 6 is screwed into the pilot hole 2 until the tip of the foundation pile 6 reaches the gravel layer 7, thereby allowing the cement-based solidification material 3 filled in the pilot hole 2 to penetrate into the gravel layer 7.

[0026] The cement-based solidification material 3 filled in the pilot hole 2 is pushed outward by the foundation pile 6, penetrates into the ground 1, reacts with the moisture in the soil, and gradually hardens. The cement-based solidification material 3 also penetrates into the gravel layer 7 below the pilot hole 2, reacts with the moisture in the soil, and gradually hardens, so that the tip of the foundation pile 6 is firmly fixed to the gravel layer 7. Furthermore, the cement-based solidification material 3 is also present around the main body 6a (between the excavation wings 6b), and the moisture inside the ground 1 penetrates into the pilot hole 2 and hardens the cement-based solidification material 3 present around the foundation pile 6, so that the foundation pile 6 is firmly fixed to the pilot hole 2 as shown in Figure 3(d). This completes the installation of the foundation piles 6.

[0027] [Fourth embodiment] A fourth embodiment of the method for installing foundation piles according to the present invention will now be described. A boring survey of the ground 1 may be conducted, and if a gravel layer 7 is not present in the ground 1, the method of installing the foundation piles 5, 6 shown in the first or second embodiment may be adopted, whereas if a gravel layer 7 is present in the ground 1, the method of installing the foundation piles 6 in the third embodiment may be adopted. In other words, the methods of the first to third embodiments may be left as options, and an appropriate method may be adopted based on the results of a boring survey of the ground 1 at the construction site. This makes it possible to handle soft ground, hard ground, and hard ground with a gravel layer 7 present, thereby improving workability. [Industrial Applicability]

[0028] INDUSTRIAL APPLICABILITY The present invention provides a method for installing foundation piles that is easy to install and can reduce construction costs, and has industrial applicability. [Explanation of symbols]

[0029] 1 ground 2 Pilot holes 3 Cement-based solidification materials 4 Improved columnar body 5 Foundation piles 5a Main body 5b feather 6 Foundation piles 6a Main body 6b Drilling wing 7 Gravel layer 8. Mixer

Claims

1. forming a pilot hole having a diameter D1 extending vertically in the ground; Filling the pilot hole with a cement-based solidification material; A step of forming a columnar improved body by stirring the ground together with the pilot hole in a range of diameter D2 larger than the diameter D1; A method for installing foundation piles, characterized by comprising at least a step of driving foundation piles into the columnar improved body before the columnar improved body solidifies.

2. 2. The method for installing a foundation pile according to claim 1, wherein the foundation pile comprises a rod-shaped main body and a plurality of wings extending circumferentially from the main body.

3. forming a pilot hole extending vertically in the ground; Filling the pilot hole with a cement-based solidification material; A method for installing a foundation pile, characterized by comprising at least a step of rotating a pile having spiral drilling wings around a rod-shaped main body as a foundation pile around its axis while screwing it into the pilot hole, thereby allowing the cement-based solidification agent filled in the pilot hole to penetrate into the ground surrounding the pilot hole.

4. forming a pilot hole extending vertically into a ground having a gravel layer therein, the pilot hole reaching the gravel layer; Filling the pilot hole with a cement-based solidification material; A method for installing a foundation pile, characterized by comprising at least the step of using a pile having spiral drilling wings around a rod-shaped main body as a foundation pile, rotating the foundation pile around its axis and screwing it into the pilot hole until the tip of the foundation pile reaches the gravel layer, thereby allowing the cement-based solidification agent filled in the pilot hole to penetrate into the gravel layer.

5. A method for installing foundation piles, comprising: conducting a boring survey of the ground; and if a gravel layer is not present in the ground, employing the method described in any one of claims 1 to 3; and if a gravel layer is present in the ground, employing the method described in claim 4.

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